Cutting out the Yahoo Groups banner in Gnus

One of the nice things about Gnus is that you can have it automatically remove junk from the messages you read. Such junk includes banner advertisements at the bottom of messages. One obnoxious example is the block that gets tagged on to the bottom of every message that comes from a Yahoo! Groups mailing list. I read a few such mailing lists, including the one for del.icio.us. It looks like: